A network element can include two different planes that are used to process network traffic, a control plane and a data plane including one or more hardware forwarding engines. The data plane receives, processes, and forwards network traffic using various configuration data (e.g., forwarding, security, quality of service (QoS), and other network traffic processing information). The control plane controls these processing functions of the data plane by configuring the data plane, managing data collected by the data plane, monitoring the data plane, and other management functions. The functions for each of the data and control planes are programmed by a software image that is stored on the network element. When the network element boots up, the software image is loaded and is used to program the data plane and control plane.
Periodically, the software image is updated. For example, the network element is upgraded to a new software image to add new features and/or fix problems with the current software image. Alternatively, the network image can be downgraded to a previous version of the software image. To change the software image, the network element loads the new software image, marks this new software image as the current software image, and reboots the network element. As the network element boots up, the new software image is loaded and programs the control and data planes of the network element.
A problem with this way of upgrading or downgrading the software image is that, by rebooting the network element, the network element is inoperable for a relatively long time. For example, rebooting the network element can cause the network element to be off-line for upwards of five minutes. During this off-line time, the data processing functions of the network element are inoperable. This can lead to an interruption of data networking services that rely on the network element.